Large scale operations involving massive rock-blasting for mining and other purposes, in recent years, have led to the use of relatively large and deep boreholes which are filled with blasing agents and set off in groups, sometimes in large numbers. In many cases, these boreholes become filled or partly filed with ground water before they can all be loaded with the explosive materials and set off at proper times. It is desirable, in such cases, to remove all or most of the water before loading, especially when the explosive blasting agents are such as to be adversely affected by water. Various types of pumps and other water lifting devices have been used or proposed for this purpose. Many of these are too heavy, complex or cumbersome for efficient field use.
Some suggestions have been made in the prior art, however, for the use of relatively small and light weight water lifting or ejecting systems. Small submersible pumps are sometimes used but their power lines and the necessary piping or conduits make 101, unhandy. Moreover, their capacity is often quite small or they are too large to use in typical boreholes. In U.S. Pat. No. 3,764,235, to Bittermann, a portable pneumatic device having an inflatable structure and means for driving borehole water through it is described. This deivce is relatively small and comparatively easy to handle for the purpose. It comprises a hollow elastic bore-plugging body which can be set into a borehole and inflated, thus expanding to plug the hole. When the inflating pressure inside the body reaches a predetermined maximum, a pressure relief valve opens, allowing compressed air to escape downwardly to force the water below the body out of the hole through a conduit.
The present invention is an improvement over the type of device just described. It avoids, however, the relative movement between the body ends in the Bitterman device, which tends to dislodge the body from its hole-plugging position. It also avoids the necessity for using complicated parts, such as a pressure relief valve, and it starts putting water-expelling pressure into the lower part of the borehole almost immediately, instead of waiting until the device is fully inflated and until a predetermined pressure is built up inside the body. The device of the present invention also is designed to fully expel the water in the outflow by a sudden expansion or "blow-out", which occurs as soon as the water level in the hole reaches the desired low level. This avoids run-back of water in the line to the hole, which usually occurs when the prior art pumping operations are discontinued. It is, therefore, an object of the present invention to provide an inexpensive apparatus and an efficient method for complete borehole dewatering operations.
Many blasting holes are bored in rock formations which contain fissures, cracks, holes, or porosities such that pneumatic pressure in the hole below the plugging body cannot be maintained on the water column long enough to expel the water effectively. A further purpose of the present invention is to enclose the inflatable dewatering unit in such a way as to close off such leaks.
In deep boreholes, the force required to lift water out tends to push the plugging body upwardly and out of the hole. This demands that the body be anchored sufficiently firmly that such lifting cannot occur and a further object of the present invention is to so design the body that it will be firmly retained against a heavy lifting thrust. This accomplished in part by the design of the body itself and in part by the control of expanding and locking forces generated within the body, as will be further explained. Those parts of the body that engage the borehole sidewalls by friction are made preferably of materials which have high coefficients of friction against rock, including wet, slimy and dirty rock. By fixing the upper and lower ends of the plugging body or "pump body", as it may be called, so that there is relatively no movement between these ends, and by making the longitudinal gripping surfaces as long as convenient, and/or as effective as possible in gripping the borehole walls, axially of the borehole, plus the choice of high friction gripping surface materials, this object is achieved.
Another aspect of the invention, includes a reinforcing and preferably flexible cage structure for limiting expansion of the inflatable body within safe limits.
A further feature of the invention involves the design by means of which a complete blow-out of water in the outflow line is accomplished while, at the same time, the borehole is automatically depressured. Thus, the unit can be removed immediately after blow-out and taken to another hole, whereas some of the prior art devices which require set pressure relief valves, etc., must first be deflated in a separate operation before they can be removed and used in another hole.
Further features and objects of the invention will be more fully described and appreciated in the detailed description which follows.